Only valid for active forum users. Active means at least 30 postings within the last 30 days (no spam postings). This will automatically being checked at www.starbike.com shopping basket so make sure that you are logged in at the WW board!If there does not appear a WW discount position when you check out you do not have enough postings!

Downsizing my frames (from 54-56 to 52cm) and trying to figure out what is the next bikeAlready went from BMC Team Machine SLR01 55cm to Colnago C59 53cmThis one stays in Mallorca

Where is live and do most of my training is flat like a pan!Hence considering an aero frame. Must be decently comfortableIn the absence of my current bikes (sold Parlee Z4) I ride Colnago Master steel frame which is soooo comfy, bumps are very well muted.

Neither of the bikes you pointed out are going to be anywhere near the top of aero segment. Come on, comparing your tubing to a 4 digit NACA? Child's play and was eclipsed over 10 years ago on the original Cervelos. Boundary layer trips? On tubes that already encounter turbulent flow and whatever laminar section they have would transition almost immediately anyways by 20% x/c? OK

Only ones I consider to be truly aero. Felt AR has great reviews regarding comfort. New S2 was wonderful when I rode it, too

+1. I agree with this, especially if one wants a truely aero road frame. If you want a semi aero frame you can throw in the Venge, Propel, Foil...etc. Cervelo and Felt are the leaders in aero in my opinion.

So between an ESX and S5, I would say S5 hands down keeping everything else equal (geometry works for you, pricing...etc.).

"Marginal gains are the only gains when all that's left to gain is in the margins."

Ride an S5 before you buy one. I rented on on holiday and put a few hundred miles on it and it was by far the worst handling bike I have ever ridden. It motors in a straight line, but feels terrible climbing, descending, turning, etc. I read that they finally shortened the ridiculously long head tube on the future S5, so the new ones might be better (the head tube was not the only problem I had with the bike).

I know there are a lot of other potential reasons, but no one on Garmin rides the S5 anymore, instead opting for the S3. This might be marketing on Cervelos part or it might be because they all felt the same way as I did about the S5. Something to think about.

That is a valid concern. I believe Felt did this as not having the traditional rear brake allowed them to fine tune the seat stays for more comfort as they didn't need the brake stay or have it built up for having a rear brake. So that is one benefit of moving the rear brake to the bb. However that has its own issues. But if you aren't racing with a pro team and need a mechanic to work on the bike from the team car, I think for the most part it should be fine. You set it and forget it.

From your list of bikes, I would go Cervelo S5 hands down. Especially if you are considering the new 2015. Much better than the ESX imo.

I can't remember the exact number given but I want to say an integrated front brake saves you 5-6 watts from what Dave Koesel and Damon Rinard have posted. However, one has to consider the performance (or lack thereof) that comes with an integrated front brake. You can get an aero mechanical/hydraulic front brake that will gain you some of the aero back while still offering good performance.